The present invention relates to a pressure control device for brake systems of automotive vehicles including a stepped control piston which cooperates with a valve element to control pressure medium passage between an inlet and an outlet chamber.
Such a pressure control device is known from the Published German Patent Application DE-OS No. 32 43 053 where the valve element is designed as an inertia element which upon a certain deceleration being reached, abuts on a valve seat provided on the control piston. As soon as this operating position has been reached, the control piston functions as a hydraulic transmission piston so that the outlet pressure is reduced with respect to the inlet pressure by the ratio of the cross-sectional surfaces of the stepped piston.
The disadvantage of a control device of this type is the change-over pressure dependence on the viscosity and on the flow rate, and the fact that the reduction ratio will be constant after the deceleration-responsive change-over pressure has been reached. As a consequence, it is impossible to adapt the rear axle braking pressures optimally to the specific requirements of the vehicle.
It is, therefore, an object of this invention to provide a pressure control device of this type which, in addition to a simple construction, is characterized by a reliable operation which is independent of temperatures and flow rates. Moreover, an optimum adaption of the characteristic line to the specific requirements of the vehicle is provided.